A conventional image forming device includes an image carrier on which an electrostatic latent image is formed, a toner cartridge which stores toner to be used for development of the electrostatic latent image, a developing roller which charges the toner and allows the charged toner to be adhered to a surface of the image carrier to develop the electrostatic latent image, a developing cartridge detachably attached to the toner cartridge and including the developing roller, and a transfer unit which transfers the toner adhered on the image carrier to a recorded medium.
In this kind of image forming device, when the electrostatic latent image is formed on the image carrier, the developing roller charges the toner, allows the charged toner to be adhered to the image carrier and develops the electrostatic latent image. Subsequently, when the transfer unit transfers the toner adhered on the image carrier to the recorded medium, an image corresponding to the electrostatic latent image is formed on the recorded medium. Since the toner cartridge is detachably attached to the developing cartridge, the toner cartridge can be exchanged when the toner is exhausted.
Japanese Patent Application Publication No. Hei09-319201 discloses an image forming device having an agitator provided in the toner cartridge to feed the toner stored in the toner cartridge to the developing cartridge, while agitating the toner; and an auger provided in the developing cartridge to conveying the toner within the developing cartridge. In this case, by driving the agitator and the auger simultaneously, the toner is circulated between the developing cartridge and the toner cartridge. Therefore, the toner is prevented from concentrating at one point and/or becoming hardened, resulting in that liquidity of the toner is ensured to improve the image quality.
Japanese Patent Application Publication No. Hei9-319202 discloses an image forming device having a toner cartridge with a feed port and a return port and an agitator, and an auger. The feed port is formed at one end of the toner cartridge in an axial direction of a developing roller to face the developing cartridge and feed the toner into the developing cartridge. The return port is formed at the other end of the toner cartridge in the axial direction to face the developing cartridge and return the toner into the toner cartridge. The agitator is provided inside the toner cartridge to agitate the toner. The auger conveys the toner along the axial direction in the developing cartridge, while mixing the toner. Therefore, some of the toner which has not been adhered to the developing roller is returned to the toner cartridge. In this way, the toner is circulated between the developing cartridge and the toner cartridge by the auger and the agitator.
The image forming devices such as a laser printer and a facsimile machine are often used on a desk in an office. Thus, there is a demand for manufacturing a compact-sized image forming device.
An object of the invention is to provide a toner cartridge and a developing device including the same that circulates the toner between the toner cartridge and the developing cartridge in a down-sized image forming device.